Method of treating cast iron



Patented July 21, 1942 METHOD or TREATING CAST IRON Charles 0. Burgess,

tion of West Virginia No Drawing. Application February 6, 1940, Serial No. 317,525

6 Claims.

The invention relates to the manufacture of cast iron, and provides a new and useful method of making cast iron.

Although research and invention have succeeded in broadening the usefulness and in improving the quality of cast iron, largely by providing a better understanding of cupola operation, proper selection of base mixtures, and correct employment of additions of such elements as chromium, nickel, and molybdenum, considerable difiiculties in the founding of iron remain to be overcome.

Of these difliculties, the greatest is probably the sensitivity of cast iron to variations in wall thickness (or rate of cooling). For example, if a cast iron be selected that is gray throughout a one-quarter inch section, in a one or two inch sectio'nit will ordinarily be weak and opengrained and have a low resistance to wear. Conversely, if the percentages of carbon and silicon be adjusted to improve the physical properties in heavy sections, the cast iron will tend to chill to a white or mottled iron in the thinner sections, thereby tending to produce brittle, poorly machinable portions. In practice, strength and soundness in heavier sections are often sacrificed in order to insure machinability of the entire casting. Moreover, the sensitivity of cast iron to variations in wall thickness imposes limitations on the design of cast iron articles.

Of the methods heretofore proposed to ameliorate this condition, those most widely used are three in number. The first comprises the use of irons ofdiflerent analysis for castings of different sections. One serious difliculty encountered in using this method is that of identifying the iron from a specific cupola charge and of drawing a. clear dividing line between the products of successi e cupola charges. The second method involves melting down in the cupola an iron of average or intermediate composition, and adjusting the percentages of silicon and carbon in individual ladles so as to produce irons suitable for sections of various thicknesses. This latter method is usually only approximate in its results, because of the difficulty of quickly and accurately estimating weights and compositions.

The third method comprises the addition of small quantities of silicon or calcium silicide to a relatively low-silicon iron while the latter is in the ladle, just before pouring. This method has been widely adopted, despite the fact that it requires extremely accurate control of analysis and of melting conditions, largely because it affords greater latitude in the diversity of section Niagara Falls, N. Y., assignor to Electro Metallurgical Company,

sizes that may be cast from a single batch of cast iron.

It is an object of this invention to provide a.

- cooling or in wall thickness while maintaining or improving its strength, ductility, and resistance to wear.

In accordance with the invention, these objects are attained by adding to cast iron while it is molten, and preferably just before casting, a composition of 'matter comprising as its essential ingredients iron, silicon, calcium, and one or both of the metals vanadium and titanium, and preferably also manganese. The ingredients should be in intimate association, as by mechanical admixture, and are preferably alloyed with each other at least in part.

The silicon content may be between 25% and 85%, and is preferably between and 80%. The iron shpuld not exceed and preferably does not exceed about 45%. The calcium content may be between 1% and 16%, and is preferably between 2% and 6%. The total percentage of vanadium or titanium, or of both these elements, may be between 1% and 20%, and it should ordinarily be between 3% and 10%, although on occasion it may be as high as 25%. As between vanadium and titanium, vanadium is preferred. When manganese is present, it should ordinarily be between 1% and 15%, preferably between 3% and 10%, but may sometimes be as much as 25%. It is preferred that no one of the elements calcium, vanadium, titanium, or manganese be more than 25% of the total 'addition of silicon, calcium, vanadium, titanium and manganese.

. In general, the greater the number of ingredients, chosen from among those mentioned above, the better the quality of the'cast iron. Thus, a. preferred composition of the invention comprises 60% to silicon, 1% to 4% cal-' cium, 5% to 10% vanadium, 4% to 10% manganese, remainder iron.

A part, preferably less than half, of the calcium may be replaced by one or more of the metals barium, strontium, magnesium, and beryllium. Likewise, a part, preferably minor, of the vanadium may be replaced by one or both of the elements columbium and tantalum. Further, a minor part of the titanium may be replaced by cerium or thorium.

Although the amount of the composition of the invention to be added to the molten cast iron will vary considerably, depending chiefly on the type of cast iron being treated, the analysis of the composition of matter added, and the properties desired in the final product, it will ordinarily be best to add enough to increase the silicon content of the casting by from 0.05% to 1%, about 0.5% being of wide suitability.

In applying the method of the invention to standard foundry practice, it will usually be desirable to reduce the silicon content of the cupola charge so that the ladle addition of the invention will bring the silicon percentage tothe neighborhood of that usual in standard practice. But it will frequently be found advantageous to adjustthe cupola charge and ladle addition to give a silicon content substantially higher than customary.

The relative efiectiveness of this invention is illustrated by the data set forth in the following table. These data were obtained by preparing in the high frequency electric induction furnace, cast irons of accurately-controlled similar compositions. Just before casting each sample of iron, enough special addition alloy was used to add the indicated percentages of the elements silicon, calcium, and vanadium. The addition alloy used in making cast iron No. 1 was silicon metal containing over 98% silicon; that used for cast iron No. 2 was an alloy containing 45% silicon, 4.9% calcium, 19.8% vanadium, remainder iron. The final cast iron in each case contained the indicated percentages of total carbon and silicon. The heats were cast into standard (A. S. T. M.) arbitration bars, tensile strength test samples, chill-depth test specimens, and step-bars. The transverse strength (Trans) is given in pounds as determined at the center of an 18-inch span. Deflection (Dell) is in inches on ltlhe 18-inch span. Depth of chill (Chill) is in me es.

The invention is applicable not only to plain cast irons but also to cast irons containing the customary alloyed additions such as chromium, molybdenum, and nickel. When used in this connection, it will often be advantageous to add one or more of these elements in admixture, or alloyed, with the composition of matter of this invention. In such instances, the added element should replace part of the silicon or iron rather than of the ingredients manganese, calcium, vanadium, and titanium. Chromium and molybdenum tend to increase the sensitivity of cast iron to variations in rate of cooling. This tendficient to increase ency may be to a great extent offset by applying the principles of this invention, thereby further extending the usefulness of chromium and molybdenum additions in cast iron.

I claim:

1. Method of treating molten cast iron which comprises adding thereto a small amount, sufficient to decrease the sensitivity of the cast iron to variations in rate of cooling, of a composition of matter containing at least one metal of the group vanidium and titanium, the total percentage of saidmetal or metals being between 1% and 25%, 1% to 16% calcium, remainder principally iron and silicon, the iron content being less than and the silicon content being greater than 25%.

2. Method of treating molten cast iron which comprises adding thereto a small amount, sufficient to decrease the sensitivity of the cast iron to variations in rate of cooling, of a composition of matter containing about 3% to 10% vanadium, 2% t0 6% calcium, remainder rincipally iron and silicon, the iron content being less than 45% and the silicon content being greater than 25%.

3. Method of treating molten cast iron which comprises adding thereto a small amount, sufthe silicon content thereof by at least 0.05% but not by more than about 1%, of a composition of matter containing about 3% to 10% vanadium, 2% to 6% calcium, remainder principally iron and silicon, the iron content being less than 65% and the silicon content being between 60% and 4. In the method of making cast iron castings which comprises producing in the cupola an iron containing less silicon than is desired in the casting, and adding ferro-silicon to such iron just before casting in an amount sufiicient to raise the silicon content to the percentage desired in the casting, the improvement which comprises adding to the iron, simultaneously with the addition of ferro-silicon and in intimate association therewith, vanadium and calcium, each in an effective amount at least 1% but not over about 25% of the total addition of silicon, vanadium, and calcium. &

5. Method of treating molten cast iron which comprises adding thereto an amount, sufficient to increase the silicon content thereof by between about 0.05% and about 1%, of a composition of matter containing between 25% and silicon, 1% and 25% of at least one metal of the group vanadium and titanium,.l-% and 16% calcium, 1% and 15% manganese, remainder substantially all iron, the iron content being less than 45%.

6. Method of treating molten cast iron which comprises adding thereto an amount, sufiicient to increase the silicon content thereof by between about 0.05% and about 1%, of a composition of matter containing between 60% and 80% silicon, 5% and 10% vanadium, 1% and 4% calcium, 4% and 10% manganese, remainder iron.

CHARLES O. BURGESS. 

